The goal is to determine the mechanism(s) by which luminal products of digestion induce gut peptide release. Primary cultures of isolated enriched dog colonic endocrine cells that contain peptide YY (PYY) and glucagon-LI (GL-29LI) immunoreactivity will be used as a model system. Cells from the mucosa will be dispersed, separated by elutriation and cultured for 48 h. With the use of highly specific antisera for PYY and GL-29LI, the secretory response of these enriched endocrine cells will be monitored during incubation with various luminal agents. It will be determined if nutrients such as fatty acids or amino acids directly stimulate PYY or GL-29LI release and if there is modulation mediated by adrenergic or cholinergic agonists, or by hormones such as gastrin, bombesin or somatostatin. Receptor occupation or internalization of the secretagogues will be determined by both competitive receptor binding assays and with light and electron level autoradiography of the cultured cells. Receptor binding or internalization of nutrients or secretagogues will also be examined, and correlated with adenylate cyclase activity, cAMP concentration, and peptide release. In other experiments the significance of colocalization of PYY and GL-29LI within a subpopulation of cells will be studied. Colocalization will be established using antisera labelled with colladal gold. With the use of scanning and transmission electron microscopy it will be determined if PYY and GL29-like peptides are differentially compartmentalized within the cell and if this is reflected by contrasting mechanisms of release. These studies will extend our knowledge about the colon as an endocrine organ. PYY is thought to be both the "pancreotone" or "anti-cholecystokinin hormone", and an enterogastrone. As such it may play a key role in the control of pancreatic and gastric secretion. Enteroglucagon in turn is thought to be trophic to the small intestinal mucosa and it is thought that the "adaptive hypertrophy" seen in the short bowel syndrome is a result of increase of its release. These studies should advance our understanding of the factors controlling the release of these two important ileo-colonic hormones.